【作者】 蔡立君；

【导师】 周仲荣；

【作者基本信息】 西南交通大学 ， 机械设计及理论， 2007， 硕士

【摘要】 作为最轻的金属结构材料，近年来镁合金在汽车、航空航天、家用电器等行业得到了广泛运用，其各种摩擦磨损问题也日益凸现，然而目前有关其磨损机理的研究还主要集中在滑动磨损，对法向冲击下磨损机理的研究几乎还未见报道。目前已有由镁合金制造的发动机箱体和变速箱等汽车零部件，本文拟模拟此类镁合金零部件可能遇到的振动冲击现象，研究镁合金在冲击条件下的损伤机理，探讨影响镁合金冲击磨损性能的因素，具有重要的实际意义和理论意义。本文利用自制的冲击磨损试验机，对ZM5镁合金及其微弧氧化陶瓷层进行了试验研究。系统地考察了载荷及冲击次数对冲击磨损行为的影响；借助激光共焦显微镜、X射线衍射仪、扫描电子显微镜、能谱仪及表面轮廓仪等对磨损深度、面积及表面形貌进行测量分析，探讨了冲击磨损机理，得出如下主要结论：1．冲击磨损是磨损与疲劳的复合过程。对镁合金基体而言，其损伤主要表现出疲劳的特征，磨损深度及面积随冲击次数的增加而非线性增加。冲击磨损初期的主要损伤形式是塑性变形和塑性堆积，且变形深度增加较快；随着冲击次数的增加，在冲击坑边缘和中心之间开始出现粘着磨损，并伴有撕裂的特征；后期由于材料表层产生加工硬化，深度增加速率减缓，表面及次表层裂纹萌生，裂纹扩展相交后导致材料发生疲劳剥层失效，由LCSM测得的剥层厚度约为0.7μm。2．镁合金微弧氧化陶瓷层由最外层疏松层、中间层致密层及界面层组成。冲击过程初期，疏松层中大量微凸体首先与冲头接触，在反复冲击力作用下被破坏，表面材料或剥落，或向对磨件转移，造成初期磨损量较大，磨损深度曲线增加较快；随后过程中，试样间接触应力减小，磨屑层形成以及基体塑性变形抗力提高等因素使得后期磨损深度及面积增加减缓。陶瓷层损伤是磨损与疲劳交替作用造成的，即其冲击磨损呈现这样一个过程：磨屑形成-磨屑层形成-磨屑层疲劳剥落-新的磨屑形成-新磨屑层形成-磨屑层再剥落。3．在本试验的两种冲击载荷下，镁合金微弧氧化陶瓷层的磨损深度及面积均大于镁合金基体，并且，陶瓷层的磨损速率比基体的磨损速率快。试验结果表明，与滑动磨损情况不同，法向冲击下，原位生长的微弧氧化陶瓷层的存在并没有起到减轻冲击磨损的作用。更多还原

【Abstract】 As the lightest structural metallic materials, magnesium alloys have been used broadly in the automobile, aerospace and household appliances industries, at the same time, kinds of friction and wear problems are also emerging. While up to now, the research on the wear mechanism of magnesium alloys has been focused on sliding wear, few publications on the wear mechanism under normal impact are found in literatures. Nowadays, there have been automotive parts and components made of magnesium alloys, such as engine case and gearbox. Therefore, simulating the vibration impact phenomenon which appears when the engines work, the damage mechanism of magnesium alloys under impact condition has been investigated in this thesis, and the factors influencing the wear performances have been discussed. So the study has both practical significance and academic value.The impact wear tests of ZM5 magnesium alloy and its micro-arc oxidation (MAO) ceramic coatings have been performed by a specially designed ball-on-flat impact tester. The influences of test load and impact number on impact wear behaviors were investigated, and the wear depth, wear area and surface pattern were measured and analyzed by means of laser confocal scanning microscope (LCSM), X-ray diffraction (XRD), scanning electrical microscope (SEM), energy dispersive spectroscope (EDS) and Surface Profiler. Main conclusions were obtained as follows:1.The process of impact wear was a compound process of wear and fatigue. The damage of magnesium alloy mainly puts up the characters of fatigue, and the wear depth and area increased nonlinear with the increase of impact number. During the earlier stage of impact wear, plastic deformation and accumulation were the main form of damages, and the wear depth increased rapidly. With the proceeding of impact process, the phenomenon of adhesive wear appeared between the center and edge of impact wear scar. During the later stage, because of the work-hardening of surface layer, cracks initiated at the surface and subsurface, then delamination occurred due to the propagation and intersection of cracks. The thickness of delaminated layer measured by LCSM was about 0.7μm.2.The MAO ceramic coating was composed of three layers, from outer to inner, they are loose layer, compact layer and interface layer. For the earlier stage, a large number of asperities in the loose layer were damaged by the impact force, and then the surface materials were either flaked off as wear debris or transformed to the counterparts. With the proceeding of test, the contact stress between the specimens decreased, the wear debris layer formed, and the resistance of plastic deformation increased, all these factors resulted in the decrease of wear depth and area. In terms of the whole impact wear process of ceramic coatings, the wear mechanism was charactered by the alternation of wear and fatigue, namely the impact wear was such a cyclic process: formation of wear debris, formation of wear debris layer, fatigue delamination of wear debris layer, formation of new wear debris.3.Contrast the experiment results of magnesium alloys with that of MAO ceramic coatings, we could found that under two kinds of impact loads, the wear depth and area of MAO ceramic coatings were both larger than that of magnesium alloy. The results indicated that different from the sliding wear, the existence of in situ produced MAO ceramic coatings didn’t alleviate the wear of magnesium alloy.更多还原